Regulatory proteins of lobster striated muscle.

The regulatory proteins of lobster muscles consist of tropomyosin and of troponin. Troponin contains a 17,000 chain weight component, two closely related components of about 30,000 and a 52,000 chain weight component. In addition to troponin, tropomyosin is required for the inhibition of the magnesium activated actomyosin ATPase activity in the absence of calcium and for the reversal of this inhibition by calcium. Lobster tropomyosin interacts with rabbit actin and lobster troponin interacts with rabbit tropomyosin. The 30,000 doublet component corresponds to the troponin-I of rabbit and inhibits the ATPase activity of actomyosin both in the presence and in the absence of calcium. The 17,000 component corresponds to the troponin-C of rabbit; it binds calcium and reverses the inhibition of the ATPase activity by troponin-I in the presence of calcium. No more than 1 mol of calcium is bound by a mole of troponin-C or by troponin. The 52,000 component interacts with tropomyosin and has been tentatively identified as troponin-T; however, it has not been demonstrated as yet that this component had a role in the regulation of lobster actomyosin.     

The mechanochemistry of cardiac muscle. I. The isometric contraction

The utilization of creatine phosphate (CP) and adenosine triphosphate (ATP) was studied in the iodoacetate (IAA) and nitrogen (N₂)-treated cat papillary muscle. Under these conditions the net production of ATP does not occur, and the net utilization of ATP is reflected in a fall in CP concentration. The rate of energy utilization of the IAA-N₂-treated cat papillary muscle resting without tension was 0.68 µmole CP/g/min. This rate was increased to 1.07 µmole/g/min when muscles were passively stretched with 2 g of tension. In a series of isometrically contracting muscles CP utilization was found to be proportional to the number of activations and the summated contractile element work. These rates of CP utilization were 0.083 µmole/g/activation and 0.0059 µmole/g-cm of work. The calculated mechanochemical coupling efficiency was 33%.     

Proteomic analysis of striated muscle

The techniques collectively known as proteomics are useful for characterizing the protein phenotype of a particular tissue or cell as well as quantitatively identifying differences in the levels of individual proteins following modulation of a tissue or cell. In the area of striated muscle research, proteomics has been a useful tool for identifying qualitative and quantitative changes in the striated muscle protein phenotype resulting from either disease or physiological modulation. Proteomics is useful for these investigations because many of the changes in the striated muscle phenotype resulting from either disease or changes in physiological state are qualitative and not quantitative changes. For example, modification of striated muscle proteins by phosphorylation and proteolytic cleavage are readily observed using proteomic technologies while these changes would not be identified using genomic technology. In this review, I will discuss the application of proteomic technology to striated muscle research, research designed to identify key protein changes that are either causal for or markers of a striated muscle disease or physiological condition.     

The transformational potential of striated muscle in hydromedusae.

Isolated striated muscle tissue of the Anthomedusa Podocoryne carnea participates in the regeneration of a functional manubrium (the feeding organ of medusae) when it is combined homoclonally with endodermal cells of the medusa umbrella. The morphogenetic potential of striated muscle cells in this regeneration process was evaluated by combining nuclear labeled striated muscle cells with some unlabeled endoderm cells. Histological and autoradiographical results demonstrate that transformation of striated muscle cells into smooth muscle cells of the ectoderm and also into endoderm cells must have occurred in the regenerate. The potential for cell transformation of isolated striated muscle cells of Podocoryne carnea is discussed and it is postulated that under appropriate conditions all cell types necessary for the regeneration of a manubrium can be formed from striated muscle cells.     

Interfilament forces in striated muscle

Evaluation of the Van der Waals energy per filament suggests that molecular dispersion forces should not be very important in determining the stability of the myofilament lattice in resting muscle. In order to explain the lattice stability and other important properties of the striated muscle, it is suggested that a balance between electrostatic forces and forces developed by some interfibrillar structures is mainly responsible.     

Regulation of vertebrate striated muscle contraction

Most current textbooks of cell biology and histology use the steric blocking model to describe the protein mechanism by which vertebrate striated muscle contraction is regulated. Evidence accumulated in the past decade, however, reveals the regulation of muscle contraction to be far more complex than this model predicts.     

MCT1 confirmed in rat striated muscle mitochondria.

We sought to test the hypothesis that monocarboxylate transporter isoform 1 (MCT1) is the inner mitochondrial membrane lactate/pyruvate transporter, and, as such, contributes to functioning of the intracellular lactate shuttle. However, presence of a mammalian mitochondrially localized MCT1 (mMCT1) has been contested. We sought to confirm by Western blotting the mitochondrial localization of MCT1 in rat cardiac, soleus, and extensor digitorum longus muscles utilizing three different cell fractionation methods and three different antibodies. We performed Western blotting using antibodies to cell membrane glucose transporter isoform GLUT1, inner mitochondrial constituent cytochrome oxidase, the monocarboxylate transporter protein chaperone CD147, as well as custom and commercially available MCT1 antibodies. Western blots demonstrated similar results with each MCT1 antibody and two of three methods of fractionation. MCT1 was found in the mitochondria, as well as in the sarcolemmal membrane and whole muscle homogenates. Probing with GLUT1 and CD147 demonstrated that mitochondrial fractions were not contaminated with sarcolemmal remnants. Probing with cytochrome oxidase showed mitochondrial localization of MCT1. Comparison of these results to the findings of others indicates that the most likely source of discrepancy is the cell fractionation procedure utilized.     

Lobster (Homarus americanus) striated muscle myosin.

1. Myosin from the thin-filament regulated flexor muscle of lobster contains 2 moles of each of 2 light chains. 2. The Lb 1 light chain of 19,000 daltons which can be removed by DTNB is heavier than the DTNB light chain of chicken. The Lb 2 light chain of 17,000 daltons can be removed with urea. 3. On electrophoresis in 8 M urea (pH 8.7) the Lb 2 light chain migrates with a mobility similar to that of chicken A2, but the Lb 1 migrates significantly faster than any of the chicken light chains. 4. In lobster, the DTNB treatment destroys the Ca and K-EDTA ATPase activity of lobster myosin.     

Gene targeting restricted to mouse striated muscle lineage.

Spatially and temporally regulated somatic mutations can be achieved by using the Cre/LoxP recombination system of bacteriophage P1. In order to develop gene knockouts restricted to striated muscle, we generated a transgenic mouse line expressing Cre recombinase under the control of the human alpha-skeletal actin promoter. Specific excision of a loxP-flanked gene was demonstrated in striated muscle, heart and skeletal muscle, in a pattern very similar to the expression of the endogenous alpha-skeletal actin gene. Therefore, the reported transgenic line can be used to target inactivation or activation of a given gene to the skeletal muscle lineage.     

Structural changes in thin filaments of crab striated muscle.

Low angle X-ray diffraction patterns were recorded from crab leg muscle in living resting state and in rigor (glycerol-extracted). Both resting and rigor patterns showed a series of layer-lines arising from a helical arrangement of actin subunits in the thin filaments. In the resting state, the crossover repeat of the long-pitch actin helices was 36.6 nm, and the symmetry of the genetic actin helix was an intermediate between $\text{26}\text{12}$ and $\text{28}\text{13}$. When the muscle went into rigor, the crossover repeat changed to 38.3 nm and the helical symmetry to $\text{28}\text{13}$.In the living resting pattern, six other reflections were observed on the meridian and in the near-meridional region. These were indexed as orders of 2 × 38.2 nm and could be assigned to troponin molecules; the spacings and the intensity distributions of these reflections could be explained by the model proposed by Ohtsuki (1974) for the arrangement of troponin molecules in the thin filaments.The muscle in rigor gave meridional and near-meridional reflections at orders of 2 × 38.3 nm. These were identified as the same series of reflections as was assigned to troponin in the living resting pattern, but were more intense and could be seen up to higher orders. We consider that the myosin heads attached to the thin filament at regular intervals along its axis also contribute to these reflections in the rigor pattern.     

Myosin from striated adductor muscle of Chlamys nipponensis akazara.

Myosin was isolated from striated adductor muscle of Akazara shell-fish, and purified on DEAE-Sephadex A50. The sedimentation constant (s 20,2 0 W) and the intrinsic viscosity, [eta] of Akazara myosin thus purified were estimated to be 6.6 S and 2.10 dl/g, respectively. In many respects, Akazara myosin was similar to scallop myosin. (1) Only one size of light-chain component (17,000 daltons) was detectable in SDS-gel electrophoresis of Akazara myosin, but two types of light-chain component were seen in urea-gel electrophoresis; these were equivalent to EDTA-light chain and SH-light chain of scallop myosin. The molar ratio of heavy chain (206,000 daltons), EDTA-light chain, and SH-light chain in Akazara myosin was estimated, from the staining densities of gel-electrophoretic bands, to be approximately 1 : 1 : 1. (2) EDTA-washing procedure removed EDTA-light chain only, causing desensitization of Akazara myosin. EDTA-light chain isolated from Akazara myofibrils was able to resensitize EDTA-washed Akazara myosin. Akazara myosin, however, was found to be different from scallop myosin in two important properties: (1) complete removal of EDTA-light chains was required to achieve a complete loss of calcium sensitivity, and full resensitization was attained on recombination of EDTA-light chains with desensitized myosin prepared essentially free from EDTA-light chains. (2) EDTA-light chains isolated from Akazara myofibrils show a calcium-induced UV absorption difference spectrum.